Method for producing an electrode structure

ABSTRACT

The invention relates to a process for production of an electrode structure, including:
         a. Producing a longitudinal body having a core and at least one layer made of an electrode material surrounding the core;   b. Removing a part of the layer made of electrode material while forming a plurality of electrodes that are arranged such as to be distributed in the longitudinal direction and which are separated from each other, and contact paths that extend in the longitudinal direction and adjoin the electrodes, each, as the same part;   c. Applying a layer made of a polymeric material while embedding, at least in part, the electrodes and/or contact paths formed in step b.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

The invention relates to a process for producing an electrode structureaccording to the features of claim 1 and to an electrode structureaccording to the generic part of claim 15.

EP 1 488 827 A1 describes a process for producing an electrodestructure, in particular a cochlear electrode to be introduced into aninner ear, in which a planar layer made of an electrode material isapplied onto a planar support material and is structured into individualelectrodes which are arranged such as to be distributed in alongitudinal direction and have contact paths adjoining them in the samepart.

It is the object of the invention to specify a process for producing anelectrode structure that enables the production of electrode structuresof high quality.

Said object is met according to the invention through a process forproducing an electrode structure, comprising the steps of:

-   -   a. Producing a longitudinal body having a core and at least one        layer made of an electrode material surrounding the core;    -   b. Removing a part of the layer made of electrode material while        forming a plurality of electrodes that are arranged such as to        be distributed in the longitudinal direction and which are        separated from each other, and contact paths that extend in the        longitudinal direction and adjoin the electrodes, each, as the        same part;    -   c. Applying a layer made of a polymeric material while        embedding, at least in part, the electrodes and/or contact paths        formed in step b.

In the scope of the invention, the electrodes and contacts paths areformed as one-part structures that differ from each other in their shapeand/or function, at least after step b. In this context, the contactpaths mainly serve for electrically conductive connection of theelectrodes over a spatial distance in the longitudinal direction, forexample to other conductors, a supply circuitry or the like. Theelectrodes have a different function than the contact paths. They serve,for example, for electrical connection to biological tissue, for examplenerve cells, or as a component of a sensor, in particular a sensorhaving a multi-layered structure.

The contact paths extending in the longitudinal direction shall beunderstood to mean any bridging of a distance in said direction.Pertinent examples include a straight extension parallel to thelongitudinal direction or a helical extension about the longitudinaldirection.

It it feasible, by means of the process according to the invention, as amatter of principle, to structure the electrodes directly in theirspatial position with respect to a circumferential direction about thecore. As a result, the layer surrounding the electrodes can be providedto be seamless in the circumferential direction, if needed.

Often and/or in a particularly simple design, the electrode material hasa hollow cylindrical cross-section, for example while covering acircular core. Generally, according to the scope of the invention, thelayer can take any hollow shape about a core of corresponding externalcircumference according to requirements, for example an elliptical orpolygonal cross-section.

It is generally preferred to apply the layer made of electrode materialmechanically to the core as a solid material, which attains goodstrength and flexibility and flexibility upon stress reversal of theresulting electrodes and contact paths. In principle, though, other waysof applying the layer are feasible as well, for example vapourdeposition, electroplating, etc.

It is generally preferred, but not mandatory, to use electrodestructures according to the invention on the human body. A typicalapplication is the use as a cochlear electrode in inner ear implants.Another application is as a stimulation electrode in the central nervoussystem, such as in the methods of “deep brain stimulation” in the brainor “spinal cord stimulation” in the spinal cord (pain therapy).

Furthermore, electrode structures according to the invention can serveas the basis of sensor applications, such as by building-up theelectrodes into sensors by further layers and/or overlapping design.

It is generally advantageous for electrode structures according to theinvention to have lengths in the range of 1 cm to more than 10 cm at arelative small diameter in the order of 1 mm. The high aspect ratio oflength and diameter as well as the small size of the structurescontribute to the particular suitability of the process according to theinvention. Preferred thickness values of the layer made of electrodematerial depend on the requirements and are, for example, in the rangeof 0.05 mm to 0.3 mm. This can be provided, for example, for typicalapplications for electrical connection to nerve cells. But considerablysmaller thickness values are also conceivable, for example down to lessthan 0.001 mm. Structures this thin can, in particular, be a componentof a sensor.

The electrode material preferably consists of a bio-compatible metal, inparticular for use on the human body. Pertinent examples includeplatinum and alloys thereof, in particular PtIr alloys, PtW alloys, goldand gold alloys, tantalum, titanium, niobium or other suitablematerials. Depending on requirements, the layer made of electrodematerial can just as well be composed of multiple layers made ofdifferent materials.

In a preferred embodiment of the invention, the core is removed afterstep c and the resulting hollow space is filled, at least partly, with amaterial, which preferably is polymeric, while forming a new core. Thisrenders the manufacture simple, since the core material can be adaptedto the production requirements regarding the mechanical and/or chemicalproperties. Preferably, the core to be removed later consists of ametal, in particular copper. With respect to the provision of thelongitudinal body, methods are known and established, for example fromthe field of cardiovascular electrodes, that involve the application ofbio-compatible metals, such as PtIr, by means of a drawing die onto around copper core to form a two-layer wire with a bio-compatible outerlayer. A wire of this type can serve, for example, as starting materialfor the purposes of step a. After embedding of the electrodes andcontact paths in a polymeric material, the core can be removed, forexample by etching. The resulting hollow structure is expediently beingfilled with a new core, to provide a desired mechanical property and/orto insulate the electrodes from the inner side as well. The new core canbe implemented, for example, by casting thermally or otherwise curingpolymer or by inserting a sub-calibre tube and subsequent expansion.

In an alternative embodiment, the core is not removed after step c.Cores of this type are preferably, but not necessarily, made of anelectrically insulating polymeric material, for example the samematerial as the outer polymer layer. But it is also conceivable that thecore has an inhomogeneous structure. A core of this type can consist,for example, of a metal or glass fibres, etc. on the inside and beenveloped by an insulating layer onto which the layer made of electrodematerial is applied.

In a preferred embodiment of the invention, step b. is implemented byerosive removal of the electrode material. It is particularlyadvantageous for the erosive removal to proceed by means of a laser,especially an ultra-short pulse laser, or by means of spark erosion.According to the scope of the invention, an ultra-short pulse laser, theuse of which is preferable, shall be understood to be a laser whoseenergy density is increased by temporal compression of its pulseduration. According to a particularly preferred embodiment, theultra-short pulse laser is a femtosecond laser. This allows scanning,computer-controlled processes to be used that are effective and can beimplemented in few or only one step. Modern femtosecond lasers areparticularly well-suited for metal-working, since the high energydensity results in direct sublimation of the metal removed such that theselectivity is high. In particular, the core situated under theelectrode material is affected only minimally such that undesirableeffects, such as degeneration of a polymeric core or contamination ofthe electrode material by a metallic core is minimised.

An alternative to this embodiment provides step b to be implemented bymeans of a photochemical process. Presently, a photochemical processshall be understood to be any process, in which a structured change in amaterial property is generated by means of an illumination such that amaterial can be structured by subsequent chemical process steps.Pertinent examples include photolithography processes of semiconductormanufacturing. The photochemical process preferably comprises theillumination of a layer situated on the electrode material by a laser.For example, the laser can illuminate, in a scanning andcomputer-controlled manner, a photoresist that is applied to theelectrode material. As an alternative photochemical process in place ofa gridded light beam, an imaging illumination is conceivable as well. Asan alternative to the use of a photoresist and illumination and/or as analternative to the application of a photo-chemical process, it is alsoconceivable that a masking layer for subsequent etching processes isapplied directly onto the electrode material by means ofscanning-printing processes. For further processing of electrodematerial with a textured and/or illuminated mask, please refer toprinted specification EP 1 488 827 A1 also.

It is generally advantageous to provide that step c proceeds byextrusion of the polymeric material, by printing the material, byapplication to the entire surface from liquid phase or by depositionfrom the gas phase. The polymeric material may be any polymeric materialaccording to requirements, preferably it can be bio-compatible. Examplesof suitable materials include silicone, polyimide (PI), polyurethane(PU) or parylene, in particular parylene C. The latter are depositeddirectly from the gas phase in an appropriate device and have well-knownapplications in the field of bio-compatible implants. Polyimide can beapplied, for example, in a particularly simple embodiment in the mannerof a dip coating process. Silicone and other suitable materials can beapplied, for example, by extrusion or by printing. In particular,structured scanning printing processes can be preferred presently, sincethey allow coverage of the electrode surfaces by the polymeric materialto be avoided.

It is generally advantageous for one embodiment of the invention tocomprise the step of selective removal of the layer applied in step c.,at least in regions of the electrodes. Preferable, but not necessarily,this can take place by means of a laser. In particular, this can be thesame laser, by means of which the layer was removed in step b,optionally after adjustment of operating parameters of the laser.Thereby, a galvanic contact of the electrode to the surroundings isenabled. In this sense, said step is required only if the embedding ofthe formed structures in the polymer layer took place over the entiresurface and non-selectively, but may also be desired even then for thepurpose of quality optimisation.

It is generally advantageous for the invention to comprise the step ofbending the longitudinal body about the longitudinal direction into ashape, in particular after step b or after step c. In the case ofcochlear electrodes, the shape can be a defined pre-bending into a coil.

In a possible refinement, the invention provides the layer made ofelectrode material to be surrounded by a second layer made of anelectrode material, whereby the layers made of electrode material areseparated by an insulating layer. This enables a multi-layered structurethat renders, for example, a particularly large number of electrodes andcontact paths feasible. Thus, a portion of the electrodes and contactpaths can be embedded in a first radially inner layer of insulatinglayers and another portion can be embedded in a radially outer layer.

A possible refinement of the invention provides the longitudinal body totaper at least over a section in the longitudinal direction. A taper ofthis type can be provided for example, in cochlear electrodes in orderto design the electrode structure in the inner ear region to beparticularly flexible and susceptible to minimally invasive processes.For example, the electrode can be tapered in an end section over adistance of approximately 1 cm from 1.5 mm in diameter to 0.5 mm indiameter.

Obviously, an electrode structure according to the invention cancomprise further features and process steps, such as, for example,purification steps, the attachment of a tip at one end of the electrodestructure or the connection of the contact paths to an adjoiningstructure, e.g. to a feed line or directly to a control unit.

In the case of cochlear electrodes, it is particularly advantageous forcost reasons, that the electrode structure plus the contact paths have asufficient length, for example on the order of 10 cm, to allow fordirect connection to a control unit.

The object of the invention is also met through an electrode structure,comprising

-   -   a longitudinal body having a non-conductive layer that has a        hollow shape, and    -   a plurality of electrodes that are embedded in the layer such as        to be insulated from each other, and    -   a plurality contact paths that extend in the longitudinal        direction and are insulated with respect to the outside by the        layer, and are each connected, being a single part, to one of        the electrodes,    -   whereby the non-conductive layer is formed to be seamless in        circumferential direction.

An electrode structure of this type is preferably, but not necessarily,produced by a process according to the invention.

In the scope of the invention, a hollow shape shall be understood tomean any shape of cross-section that can be selected freely depending onthe application on hand. For many applications, the insulating layerswill have a hollow cylindrical shape such that the cross-section of thelayer consists of concentric circles. In other examples, the shape ofthe cross-section can just as well be polygonal or elliptical.

Providing the layer embedding the electrodes in an insulating manner tobe seamless in circumferential direction improves the stability and/orsecurity against damage and compatibility due to the absence ofinterfering seams. The absence of seams in circumferential directionshall be understood to mean that the electrode structure comprises noseam that extend in longitudinal direction and are a disturbance asviewed in circumferential direction, at least over a substantial part ofits functionally relevant sections.

A preferred refinement of the electrode structure provides theelectrodes to each comprise a surface beyond which the surface of thelayer made of polymeric material protrudes. Preferably, but notnecessarily, an edge section of the electrodes is framed by the layer.Since the insulating layer usually consists of a softer material thanthe electrodes, this improves the compatibility. In addition, theframing of the edges reduces the risk of inadvertent projection of theelectrodes from the insulating layer, which may involve hazards whenused in the human body.

Further advantages and features of the invention are evident from theexemplary embodiment described in the following as well as the dependentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

Further features and of the can be derived from the following executionexample as well as from the attached claims.

One preferred exemplary embodiment of the invention is described in thefollowing and illustrated in more detail based on the appended drawings.In the figures:

FIG. 1 shows a schematic spatial view of an electrode structureaccording to the invention, presently for use as a cochlear electrode.

FIG. 1 a shows the electrode structure of FIG. 1 with lines hidden.

FIG. 2 shows a precursor of the electrode structure of FIG. 1 a.

FIG. 3 shows the precursor of FIG. 2 after one further process step.

FIG. 4 shows the precursor of FIG. 3 after one further process step.

FIG. 5 shows the precursor of FIG. 4 after one further process step.

An electrode structure according to the invention according to FIG. 1 isused as a cochlear electrode for implantation in the human inner ear.FIG. 1 shows a front section 1 of the electrode that is introduced intothe inner ear. With regard to diameter and material, the electrode isdesigned to have a defined stiffness in order to conform to the helicalshape in the inner ear. For this purpose, the electrode structure canjust as well be pre-bent and/or taper toward its front end.

The electrode structure 1 extends in a longitudinal direction, whereby aplurality of electrodes 2 is arranged in the longitudinal direction at adistance from each other. Presently, the electrodes 2 are provided asflat metallic plates with a rectangular circumference, but can also beof a different shape.

One contact path 3 is connected to each of the electrodes 2 such that itis the same part made of uniform material. The contact paths extend fromthe first electrode by a defined distance in the circumferentialdirection and then substantially parallel to each other and in thelongitudinal direction. Presently, the electrodes 2 and contact paths 3consist of a bio-compatible PtIr alloy. In alternative embodiments, itis conceivable that the contact paths have a different extension, forexample, a helical extension. In any case, the contact paths effectelectrical connection of the respective electrode over a distance in thelongitudinal direction in this context.

The electrodes 2 and the contact paths 3 are embedded in an outerinsulating layer 4 of the electrode structure. In this context, thesurfaces of the electrodes 2 are exposed towards the outside, whereasthe contact paths are coated with a sufficient thickness of layer 4 forinsulation.

The electrode has, at its front end, a suitably shaped tip 5, whichpresently is attached in a separate process step.

It is obvious that the electrode can extend further through at its endfacing away from the tip for basically any length. The invention canjust as well provide that only the contact paths extend further over adefined section to enable connection to an extension piece or directconnection to a control unit.

The insulating layer 4 with the electrodes 2 and the contact paths 3also envelopes a core 6 that has a circular cross-section. The core 6consists of an insulating material. In the present case, both the layer4 and the core 6 consist of bio-compatible silicone. The layer 4envelops the core in circumferential direction in seamless manner, as isalso apparent from the preferred production process described below.

A first process step a for the production of the electrode structuredescribed above comprises the provision of a longitudinal body 7 made ofa core 8 and a closed layer 9 that surrounds the core 8 and is made ofthe electrode material PtIr (see FIG. 2).

Presently, the core consists of copper and is cylindrical. The electrodematerial can be applied as a hollow cylindrical layer 9 that rests on oradheres firmly to the copper core 8 in a known manner by means of adrawing die. The diameter of the longitudinal body according to FIG. 2is typically approximately 1 mm at a thickness of the layer 9 ofapproximately 0.1 mm and corresponds to a known wire, such as is usedfor special applications in the field of cardiology.

The longitudinal body is clamped in a holder (not shown) andsubsequently the tightly adherent layer 9 is structured by means of anultra-short pulse laser for metal working. Presently, this is afemtosecond laser. Ideally, the ultra-short pulse laser causes mainlydirect sublimation of the bombarded material without evaporation from aliquid phase that is generated first. This is achieved by the highenergy density in the laser pulse and has a positive effect in that lessthermal energy is introduced into deeper layers. In this context, thelayer 9 is removed by scanning bombardment by the laser down to thecopper core 8, whereby the electrodes 2 and the contact paths 3 remainand/or are formed. A longitudinal body 7 after this processing step b isshown in FIG. 3.

Subsequently, the polymeric layer 4 made of silicone is applied ontolongitudinal body 7 that is structured in accordance with FIG. 3. Thiscan be done, for example, by extrusion or by printing-on the layer 4 bymeans of a texturing or full-surface printing process. A longitudinalbody 7 after this processing step c is shown in FIG. 4.

Subsequently, the copper core 8 is removed from the longitudinal body,for example by a chemical etching process. What remains (see FIG. 5) isthe substantially hollow cylindrical layer 4 with the electrodes 2 andcontact paths 3 embedded therein which are positioned according to thefinal electrode structure.

Subsequently, the new core 6 made of insulating material, in this casesilicone as before, is introduced into said hollow cylindrical layer 4.

Subsequently, the tip 5 can be attached such that, overall, theelectrode structure according to FIG. 1 was produced.

If the silicone was applied to the entire surface in step c, such thatthe electrodes 2 are coated with a thin polymer layer, the electrodesare exposed at a suitable place again after step c. This can be done,for example, right after step c, for example by scanning removal of thepolymer with a laser. In principle, this can involve the same laser andthe same apparatus as for production of the electrodes 2 in step b.Alternatively, this can also involve a mechanical removal. Stillalternatively, it is feasible to degenerate the polymer, i.e. presentlysilicone, with a suitable wavelength, e.g. in the UV range, instructured manner and to subsequently removed it from the electrodes bychemical means.

Depending on the choice of parameters for application of layer 4, thesurfaces of the electrodes are arranged below the surface of layer 4with the distance being the thickness of the cover that has beenremoved. If necessary, a deliberate overlap of layer 4 over the edges ofthe electrodes 2 can be effected.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1-20. (canceled)
 21. A method for producing an electrode structurecomprising: a. producing a longitudinal body having a core and at leastone layer made of an electrode material surrounding the core; b.removing a part of the layer made of electrode material while forming aplurality of electrodes that are arranged such as to be distributed inthe longitudinal direction and which are separated from each other, andcontact paths that extend in the longitudinal direction and adjoin theelectrodes, each, as the same part; and c. applying a layer made of apolymeric material while embedding, at least in part, the electrodesand/or contact paths formed in step b.
 22. The method according to claim21, characterized in that the core is removed after step c and in thatthe resulting hollow space is filled, at least partly, with a materialwhile forming a new core.
 23. The method according to claim 22,characterized in that the core consists of a metal.
 24. The methodaccording to claim 21, characterized in that the core is not removedafter step c.
 25. The method according to claim 20, characterized inthat step b is implemented by erosive removal of the electrode material.26. The method according to claim 25, characterized in that the erosiveremoval proceeds by means of a laser or spark erosion.
 27. The methodaccording to claim 26, characterized in that the removal proceeds bymeans of an ultra-short pulse laser.
 28. The method according to claim20, characterized in that step b is implemented by means of aphotochemical process.
 29. The method according to claim 28,characterized in that the layer situated on the electrode material isilluminated by a laser.
 30. The method according to claim 20,characterized in that step c proceeds by extrusion of the polymericmaterial, by printing the material, by application to the entire surfacefrom liquid phase or by deposition from the gas phase.
 31. The methodaccording to claim 20, characterized by selective removal of the layerapplied in step c., at least in regions of the electrodes.
 32. Themethod according to claim 20, comprising bending the longitudinal bodyabout the longitudinal direction into a shape.
 33. The method accordingto claim 20, characterized in that the layer made of electrode materialis surrounded by a second layer made of an electrode material, wherebythe layers made of electrode material are separated by an insulatinglayer.
 34. The method according to claim 20, characterized in that thelongitudinal body tapers at least over a section in the longitudinaldirection.
 35. The method according to claim 20, characterized in thatthe electrode structure is provided as cochlear electrode forarrangement in an inner ear.
 36. The method according to claim 20,characterized in that at least some of the electrodes are provided aspart of a sensor.
 37. An electrode structure, comprising a longitudinalbody having a non-conductive layer that has a hollow shape; a pluralityof electrodes that are embedded in the layer such as to be insulatedfrom each other; and a plurality contact paths that extend in thelongitudinal direction and are insulated with respect to the outside bythe layer, and are each connected, being a single part, to one of theelectrodes; characterized in that the non-conductive layer is formed tobe seamless in circumferential direction.
 38. The electrode structureproduced according to the method according to claim
 20. 39. Theelectrode structure according to claim 37, characterized in that theelectrodes each comprise a surface beyond which the surface of the layermade of polymeric material protrudes.
 40. The electrode structureaccording to claim 39, characterized in that an edge section of theelectrodes is framed by the layer.